Geotechnical engineering design necessitates a study of soil parameters for calculation purposes. As a complement to the conventional method, a resistivity survey can give preliminary results in a short amount of time. This study uses a statistical analysis program to show a correlation and regression for predicting soil parameters based on the resistivity value. Sixty-six data points for each soil parameter and resistivity were used for statistical analysis from six profiles of the study area as a part of the investigation. The soils are sampled by drilling the borehole up to a depth of 3 meters. The Wenner array was applied to conduct a resistivity survey. The collected data were utilized to establish a correlation between resistivity (ρ) and soil parameters such as moisture content (
 
 w
 
 ), clay content (clay), plasticity index (
 
 P
 I
 
 ), friction angle (ϕ), bulk density (γ), and porosity (n). The generated statistic model was improved through several iterations for each correlation. For the ρ-
 
 w
 
 , ρ-clay, ρ-PI, ρ-ϕ, ρ-γ, and ρ-n relationship, the total iterations are 5, 4, 7, 6, 5, and 4 for each correlation, respectively. Resistivity and moisture content showed a significant power correlation, followed by a modest relationship between resistivity and porosity. Between resistivity and other parameters, relationships such as clay content, bulk density, friction angle, and plasticity index were found to have very weak or no association. However, some trends can be seen clearly. This study aims to offer the geotechnical engineer a quick preliminary way of obtaining the associated soil parameters for various geotechnical calculations employing the resistivity approach based on the developed numerical equation.

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Soil Parameters Model Prediction via Resistivity Value Limit to Shallow Subsurface Areas

Sedimentary formations are capable of transmitting an electric current only by means of their interstitial and adsorbed water content. They would be nonconductive if they were entirely dry. A rock that contains oil and/or gas will have a higher resistivity to electric current than the same rock when it is completely saturated with formation water. The greater the connate water saturation is, the lower the formation resistivity is. This relationship to saturation makes the formation resistivity factor an excellent parameter for the detection of hydrocarbon zones. Several correlations relating the formation resistivity factor to: salinity of formation water, effective porosity, pore geometry, formation stress, temperature, interstitial fluids, and composition of rock, are discussed in this chapter. Methods for determining the formation resistivity are discussed, including: Archie equation, chemical analysis, spontaneous potential (SP) curve, and shale properties. Statistical correlations of the formation resistivity factor to several petrophysical parameters, including porosity, tortuosity, cementation factor m, water saturation, and permeability, are discussed in this chapter. Several models to estimate water saturation and flow units in shaly reservoirs are presented. Most concepts are illustrated with numerical examples. Many exercises are included at the end of the chapter.

Djebbar Tiab

Papers

Chapter 4 – Formation Resistivity and Water Saturation